This invention relates generally to internal combustion engines, valve means thereof, means for actuating the valve means, and means for controlling the actuating means. More particularly, the invention relates to a valve control system of an internal combustion (I.C.) engine which system operates to monitor and control the actuation of the valve means of the engine.
Valve control systems of I.C. engines of the type which regulates the flow rate of air supplied into an I.C. engine by controlling the opening degree of the throttle valve or an idling speed control valve installed in parallel the induced pipe of I.C. engines therewith are known. In a valve control system of this type, signals indicative of the engine operational state such as, for example, the engine (rotational) speed, are transmitted to an electronic control unit, which thereupon transmits an actuation signal for controlling the opening degree of the valve. More specifically, from a comparison of the actual engine speed and an objective speed, a feedback correction quantity is computed, and an activation signal generated in accordance with the correction for increasing or decreasing this feedback correction quantity is outputted to bring the opening degree of valve into coincidence with the objective value with respect to the operational state at the time.
However, in the event that valve means such as the idling speed control valve (ISC valve) no longer operates normally (because of a malfunctioning of the valve itself or an electrical failure such as shorting or breakage in the valve actuating circuit), and, in this state, the operation of the engine is continued., not only will the engine speed become unstable and the drivability be impaired, but accurate and positive control of operational conditions such as the engine speed and the air-fuel ratio will become impossible.
Accordingly, as disclosed in Japanese Laid-Open Patent Publication No. 95152/1985, the ISC valve is provided with a position sensor, and the valve state is judged to be normal if an objective opening degree P.sub.0 outputted from the electronic control unit and the actual opening degree P.sub.1 obtained from the position sensor are such that the relationship .vertline.P.sub.1 -P.sub.0 .vertline.&lt;.DELTA.P, wherein .DELTA.P is a certain deviation, is satisfied. If this relationship is not satisfied, the valve state is determined to be abnormal, and a measure such as notifying the operator, cutting off the fuel, or shifting to a specific operational state is carried out.
A problem which arises in a known valve control system as described above is the necessity of providing the valve with a position sensor. Another problem is that, when the temperature characteristics of the solenoid and valve error are considered, a considerably wide .DELTA.P must be set, and for this reason, even if a failure or malfunctioning occurs, it cannot be detected if the quantity .vertline.P.sub.1 -P.sub.0 .vertline. is less than .DELTA.P. Still another problem is that, because of the Construction of the valve in some cases, the objective opening degree is not attained instantaneously, and a relatively long time is required from the instant the objective opening degree is outputted until it is detected. In this long interval, the engine operational conditions change, and objective values vary successively, in which case detection of trouble becomes impossible.
Furthermore, in general, there are more cases wherein the valve fails to operate because of a break or short in the harness in the actuating circuit for transmitting electrical signals to the valve than cases of mechanical trouble of the valve itself. However, the published disclosures in the prior art indicate that the former cases have so far not received serious consideration.